WRT54G Big Problem!

Hi Guys,
Maybe you can give me a big hand on this: I bought the LINKSYS WRT54G using CABLEMODEM. and it works fine with my THINKPAD T42 laptop.

But when I use it with another Laptop (SONY VAIO VGN-NR150FE), I don't know why, the orange "Cisco Systems" light/button turn off, and the THINKPAD lost connection (WLAN light stop blinking too). After 1 min, orange ligh turn on again, and THINKPAD gets connection too, BUT WITHOUT Internet for some mins.

AND, on the VAIO, with WIreless connection, BUT without Internet Connection for some mins...